This invention relates to character recording devices in which scanning is effected with a light beam to record characters or the like as dot patterns.
More particularly, the invention relates to a character recording device in which the pulse width of a dot signal is varied in correspondence with a recording position in a picture to be recorded.
In a character recording device in which, while a recording material is scanned with a light beam such as a laser beam, the light beam is subjected to on-off modulation with the aid of a character dot signal thereby to record characters or the like as dot patterns, it is desirable that the density of the light beam be constant irrespective of its position on the recording material. However, in practice, as the light beam is moved upon the recording material, the density thereof changes for reasons to be described below. Accordingly, the recorded dots are not uniform in size as the scanning lines forming the recorded picture are not uniform in width. Especially, for scanning with a light beam, as the recording position becomes remote from the point of the recording material which corresponds to the central axis of the optical system, the density of the light beam received by the recording material decreases. As a result, the dot size in the peripheral portion of the recorded picture is reduced. That is, the width of the recorded picture is decreased.
The difference in the density of the light beam depends on the design or manufacturing accuracy of the optical system. However, in general, it is considered that the difference is due to one or more of the following reasons:
(1) The light beam scanning speed in the central portion of a region to be recorded is different from that in the peripheral portion thereof. PA1 (2) The incident angle of the light beam with respect to the recording material in the central portion of the region to be recorded is different from that in the peripheral portion. PA1 (3) In the case where the recording material has a flat recording surface, it is difficult to allow the focal plane of the light beam to coincide with the surface of the recording material over the entire region to be recorded. Therefore, the diameter of the light beam varies as the recording position changes. PA1 (4) The configuration of the light beam is irregular because of abberations in the optical system.
Accordingly, an object of this invention is to provide a character recording device which is free from the variations in the dot size with changes of the recording position on a picture to be recorded caused by any of the above-described factors.
Another object of the invention is to provide a character recording device in which characters or the like are recorded with dots uniform in size over the entire surface of a picture.